I was digging through why Google was saying "Indexed, not submitted to sitemap", and then I found a major flaw in sitemap.
From https://revi.wiki/sitemap.xml :
<sitemap> <loc> https://static.miraheze.org/reviwikiwiki/sitemaps/sitemap-reviwikiwiki-NS_0-0.xml.gz </loc> <lastmod>2021-01-30T00:57:34Z</lastmod> </sitemap>
Very first line of it:
<url> <loc>https://static.miraheze.org/wiki/About</loc> <lastmod>2021-01-29T02:05:07Z</lastmod> <priority>1.0</priority> </url>
Yes, this is linking to static.miraheze.org/wiki/About, which is.... 404.
Verified against Meta and (allthetropes sitemap generates 404, btw) spiralwiki.